We collaborated with investigators at the Fox Chase Cancer Center to study the mechanisms involved in development of B cell tumors in mice that have many histopathologic similarities to human chronic lymphocytic leukemia (CLL). The results demonstrated that the mouse tumors derived from a subset of early developing B 1 cells, and had a series of molecular features in common with human CLL including loss of a chromosomal region syntenic with human 13q14 and unmuted immunoglobulin V regions. These mice provide a novel model for understanding the pathogenesis of and developing new approaches to treatment of a subset of unmutated human CLL.A separate model for CLL was developed from studies of mice expressing an EBI2 transgene. Further studies with the Janz lab at the University of Iowa provided a new model for the human diseases Waldenstrom macroglobulinemia. We continue to be active in efforts to improve the classification systems for mouse hematopoietic neoplasms as they relate to similar human neoplasms. It is important for pathologists to be able to discriminate between hematopoietic neoplasms and non-malignant reactive lesions in the mouse and we have developed guidelines for making these determinations. Finally, we contributed to establishing a mouse lymphoma database at the Jackson Laboratory for identifying mouse models of human lymphomas.